Semchyshen et al in a paper entitled "Effects of Composition on Ductility and Toughness of Ferritic Stainless Steels" and delivered in Japan in October 1971 succinctly reviewed the status of ferritic stainless steels as follows:
"Ferritic stainless steels have long been of interest to the designer and the metallurgist because of potentially lower costs compared with austenitic grades and because of their resistance to stress-corrosion cracking in the presence of chloride ions. The factors that have prevented the wide-spread utilization of conventionally-melted ferritic grades have been limited room-temperature toughness together with embrittlement and increased sensitivity to intergranular corrosion after welding or heating at high temperatures. PA1 "As long ago as 1951, Binder and Spendelow.sup.(1) and Hochmann.sup.(2) demonstrated that the toughness of straight chromium ferritic steels was sensitive to the combined carbon and nitrogen content. Binder and Spendelow showed, for example, that the limiting carbon plus nitrogen content consistent with good toughness in a nominally 18% Cr steel was about 0.05%. A comparable value for a 25% Cr steel was closer to 0.03%. PA1 "More recently, Wright.sup.(3) confirmed a maximum carbon plus nitrogen level of 0.03% for a steel containing 26% Cr, 1% Mo and 0.22% Ti to give acceptable toughness in 3 mm-thick sheet. Somewhat higher tolerances for interstitial elements were reported for thinner sheet. PA1 "Binder and Spendelow.sup.(4) achieved low interstitial contents in vacuum-melted laboratory-scale heats by using extremely high-purity charge materials. Such a practice was, of course, not put into commercial production because its implementation would negate the economic advantages of the ferritic grades. Thus the concept of low-interstitial ferritic grades was not exploited until recent years when new steel-making techniques such as oxygen-argon melting, vacuum refining and electron-beam refining progressed to the point of economic feasibility." PA1 Chromium --21% to 30% PA1 Molybdenum --up to 5% PA1 Nickel --up to 6% PA1 Niobium --0.1% to 0.4% PA1 Aluminum --0.1% to 0.75% PA1 Titanium --up to 0.3% PA1 Carbon --up to 0.025% PA1 Nitrogen --up to 0.035% PA1 Iron --Balance
Ferritic stainless steels containing between about 12% and about 30% chromium, up to about 5% molybdenum, up to about 5% nickel and the balance essentially iron are well known in the art. Variations of this class of alloys have been developed to overcome certain disadvantages. See U.S. Pat. Nos. 3,807,991; 3,890,143; 3,929,473; 3,932,174; 3,932,175 and 3,957,544.
Although the addition of stabilizers has improved both the impact and the corrosion properties, ferritic stainless steels would find even greater use if their impact properties could be further improved. For example, ferritic steels having even better impact properties could be used in marine hardware that is utilized in colder climates, chemical processing equipment, food and beverage processing equipment, desalinization equipment, fasteners and heat exchangers and condensers.